1. Field of the Invention
The present invention relates to transfer vehicles and support systems used to transfer pallets, totes, skids and the like within a defined storage retrieval system. More particularly, the present invention relates to a system that allows precision movement, placement and replacement of both light and heavy loads in a storage retrieval system.
2. Description of the Related Art
Automated storage retrieval systems are used to retrieve and place loaded and unloaded pallets, totes, skids and the like within a predesigned storage layout. Use of such automated storage retrieval systems reduces materials handling costs by reducing personnel costs and storage floor area while simultaneously increasing flexibility within the system.
For example, in the bakery industry dough is allowed to ferment for specified times in troughs. Stackers and unstackers are used to store and retrieve the troughs in multilevel systems that decrease the floor area needed to handle a given capacity line. Such a system may include a shuttle vehicle and an on board transfer vehicle to provide random access to troughs. The storage retrieval system may be part of a larger system that transports, greases, weighs, degasses and dumps the troughs.
Other types of industrial processes may also require batch processing. For example, a container or pallet may be loaded with a substance requiring low temperature aging for a certain time. Loading the containers or pallets may take place at a loading station. The containers are then transported to a storage area. After a given time in the storage area, the containers are retrieved, transported to an unloading station and the container unloaded. The container may then be transported to a container storage area. Such functions can be highly automated with the assistance of automated storage and retrieval systems.
In order to conserve floor space, it is desirable to store loads in multilevel systems or in grids in which nearly 100% of available floor space can be utilized. If stored in grids, two load carrying devices are commonly used. A transfer vehicle is commonly used to move loads within storage lanes. To move loads between storage lanes, the transfer vehicle, supporting the load, is moved onto a shuttle vehicle that moves in a direction perpendicular to the transfer vehicle. By utilizing two load carrying devices, any location on the grid can be accessed. Such a grid allows high utilization of floor space.
In a grid system having a multitude of pallets supporting loads, pallets are constantly being moved in order to access pallets that are blocked by other pallets. The constant retrieving, moving, and replacement of pallets can be easily monitored by automated systems that keep track of each discrete pallet's location within the grid. A more difficult problem arises from cumulative placement errors that occur because of the constant pallet movement. Cumulative placement errors eventually can cause a pallet to be placed in a position that could cause a subsequent processing failure because of pallet misplacement. For example, if a tote lid must be removed, the tote must be placed within certain location parameters. If not within those parameters, the lid removal system would unable to grasp or remove the lid.
Another difficulty with such grid systems is that the transfer vehicles have relatively low load carrying capacity. Payloads are now limited to about two tons because of the load raising and lowering ability of the transfer vehicles. Many load raising and lowering systems are cam operated but as load requirements increase, cams become larger thus necessitating larger transfer vehicles which increases grid spacing and overall system cost. As increased loads require larger cams, gearboxes and motors must also increase in power and size because of the minimal mechanical advantage in cam drives. Complex hydraulic systems are more difficult and costly to control, are likely to develop leak problems and are more costly to maintain. It is most desirable to have simple systems that require little maintenance.
What is needed is a system that allows precision automated placement, movement and storage of loads. It is also desirable to have larger weight handling capacity in the transfer vehicle than is currently available. Such systems would allow higher load carrying capacity within the grid system and provide unlimited movement and placement of loads within the system without causing improper placement failures in subsequent processing operations.
Shea, U.S. Pat. No. 1,402,257, shows a freight handling apparatus used to raise and lower freight loads. A plurality of threaded rods were connected by a series of sprockets and chains
Although the prior art apparatus solved their specific problems of handling freight, the inventors were not required to address the problem of precision placement or automated load raising and lowering.